1. Field of the Invention
The present invention relates to automatic position sensing devices and more specifically to photo-optical sensing apparatus for sensing the presence or absence of an object for example paper items along a defined pathway.
2. Description of the Prior Art
Sensing devices to sense the position or movement of items along a confined pathway are well known in the art. Such devices are to be found for example in printing apparatus, copying apparatus, paper handling devices and in both liquid and gaseous transfer devices.
Many such pieces of equipment utilize mechanical micro switches. These low torque or low activation force micro switches employ spring fingers located usually in the item pathway. However, often times they are too delicate for the harsh environment within which they are employed and are susceptible to damage due to bending, breaking and flexure beyond the capacity of the metal or plastic to recover. Also, the mechanical sensitivity of such low torque switches is relatively low.
Two basic types of optical switches are known and such switches are useful in a variety of situations where mechanical switches do not work successfully or adequately or where it is desirable to avoid moving parts i.e. spring fingers, etc.
1. Reflective optical switch--Reflects light back off of an item to the light source and receptor.
2. Transparent optical switch--Attempts to transmit light through the item.
Although the reflective type switch is used it has a propensity for producing false indications or results. If, for example, colored paper is being employed or paper is used which has already been printed upon in black for example, a black square, the sensor will often produce a false trigger on the reflective mode. The sensor acts as if it sees the opposite side wall of the reflective surface, which breaks the beam being produced and indicates a false position. Additionally, many if not most of this type switch sensor require mounting brackets since none are self supporting.
Another problem associated with mechanical arm or finger wiping type switch sensors is that of the accumulation of debris or dust due to the wiping contact made by the fingers against the items. This induces false readings or signals or in some instances obliterates or surpresses the signal altogether.
All such mechanical switch sensors require a certain amount of adjustment either at the time of assembly and/or during the course of utilization. Cleaning and replacement also tend to require adjustment since the movement often quite naturally displaces the sensor relative to the item pathway however slightly.
It is an important object therefore, of the present invention to overcome these and other associated problems in a new, novel, unobvious and heretofore unknown manner by the provision of a clothes-pin-like snap-on optical sensor.
Another important object of the present invention is the provision of a snap-on sensor that is self locating and requires no adjustment once it is mounted.
It is also an object of the invention to provide an optical sensor that requires no attachment or fastening means since it is self fastening.
A still further object of the present invention is the provision of lateral edge guiding means effective to eliminate a need for horizontal lateral adjustment.
Another object is the provision of automatic locking of the sensor in place once the associated electrical harness has been attached effective to prevent accidental removal or withdrawal.
An important object is to provide an optical sensor that is relatively immune to dirt, dust and other contaminants thus eliminating the need for continual cleaning and refurbishing during extended use.